The Speed score categorizes a page as being Fast, Average, or Slow. This is determined by looking at the median value of two metrics: First Contentful Paint (FCP) and DOM Content Loaded (DCL). If both metrics are in the top one-third of their category, the page is considered fast.

The Optimization score categorizes a page as being Good, Medium, or Low by estimating its performance headroom. The calculation assumes that a developer wants to keep the same appearance and functionality of the page.

The Page Load Distributions section presents how this page’s FCP and DCL events are distributed in the data set. These events are categorized as Fast (top third), Average (middle third), and Slow (bottom third) by comparing to all events in the Chrome User Experience Report.

The Page Stats section describes the round trips required to load the page’s render-blocking resources, the total bytes used by the page, and how it compares to the median number of round trips and bytes used in the dataset. It can indicate if the page might be faster if the developer modifies the appearance and functionality of the page.

Optimization Suggestions is a list of best practices that could be applied to this page. If the page is fast, these suggestions are hidden by default, as the page is already in the top third of all pages in the data set.

Here is a screen shot of the pagespeed report for this site:

Not all sites are graded; they need enough traffic and data from the Chrome user experience report to be graded. For example, my company site has no data for pagespeed: